Method of manufacturing a composite article using fibers having optimized shapes for improved optical performance

ABSTRACT

A method of manufacturing a composite article may include providing a plurality of fibers. At least a portion of the plurality of fibers may be substantially optically transparent. The method may further include forming the fibers with at least one base surface and a pair of side surfaces oriented in non-perpendicular relation to the base surface. The method may additionally include positioning the fibers in a layer in side-by-side relation to one another such that the side surfaces overlap one another when viewed along a direction normal to a plane of the layer. The method may also include embedding the fibers at least partially in a substantially optically transparent polymeric matrix.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priority toapplication Ser. No. 12/968,557 entitled OPTIMIZED FIBER SHAPES FORIMPROVED OPTICAL PERFORMANCE and filed on Dec. 15, 2010, now U.S. Pat.No. 8,568,854, the entire contents of which is expressly incorporated byreference herein.

FIELD

The present disclosure relates generally to composites and, moreparticularly, to fiber reinforced composite articles having improvedoptical performance.

BACKGROUND

Glass is widely used as a transparency in a variety of applications dueto its superior optical qualities. For example, glass is commonly usedas a glazing material or as an architectural material for buildings.Glass is also commonly used as a transparency in vehicular applications.Unfortunately, glass is a relatively dense material and is alsorelatively brittle such that relatively large thicknesses are requiredto provide sufficient strength for resisting shattering when the glassis impacted by an object such as a projectile.

In attempts to avoid the weight penalty associated with glass,transparencies may be fabricated from polymeric materials. For example,transparencies may be formed of optically transparent monolithicpolymers such as acrylic which is less dense than glass and whichpossesses suitable optical properties. Unfortunately, acrylic is arelatively low strength material making it generally unsuitable for manyapplications where high impact resistance is required.

In consideration of the weight penalties associated with glass and thestrength limitations of monolithic polymers, manufacturers have alsofabricated transparencies from polymeric materials reinforced with glassfibers. The glass fibers may be embedded within an organic and/orpolymeric matrix to provide improved strength and impact resistance.Unfortunately, the addition of glass fibers to the polymeric matrix mayundesirably affect the optical quality of the transparency. For example,the glass fibers may have a cylindrical configuration causing each glassfiber to act as a small lens. The cumulative effect of the plurality ofglass fibers is a scattering of light as the light passes through thetransparency such that objects viewed through the transparency mayappear blurred.

In attempts to avoid the scattering of light caused bycylindrically-shaped glass fibers, manufacturers may fabricate thefibers in a ribbon shape having an elongated cross-section withgenerally planar upper and lower surfaces. In a given layer, such fibersare typically spaced apart from one another resulting in some of theincident light passing between the fibers without going through thefibers. When there is a mismatch in the refractive index of thematerials, there is a deleterious effect on the optics of thetransparency due to the more rapid phase advance of a light wave of theincident light when the wave front passes through the material having ahigher refractive index. The consequence of the incident plane wave oflight is that the wave front will become distorted and lead to opticalscatter and blurring when an image is formed. The cumulative effect in amulti-layer composite panel is that an incident wave front will becomeprogressively more distorted as the wave front passes through anincreasing number of layers of the transparency. The greater thequantity of layers in the transparency, the greater the amount ofoptical distortion in the wave front resulting in greater opticalscatter and blurring.

A further drawback associated with flat or ribbon-shaped fibers is thatthe side surfaces of the fibers may be rounded. Unfortunately, therounded side surfaces result in unwanted refractive wave steering of thelight which causes significant optical distortion when the refractiveindex of the fiber is different than the refractive index of the matrix.Manufacturers may also fabricate the fibers with squared-off sidesurfaces oriented generally perpendicular to the planar upper and lowersurfaces. Unfortunately, when the side surfaces are viewed off angle,differences in refractive index of the fibers and matrix will result inoptical distortion due to refractive and diffractive effects.

Although the fibers and the matrix may be selected to have generallymatched refractive indices at a given temperature, changes intemperature of the composite article may result in differences inrefractive index if the fibers and matrix have different temperaturecoefficients of refractive index. Furthermore, the refractive index ofthe fibers and matrix may differ as a result of residual stresses thatmay be induced in the fibers or matrix during manufacturing.

As can be seen, there exists a need in the art for a transparentcomposite article having a fiber configuration that provides improvedoptical performance over a wide temperature range despite difference inrefractive index of the fibers and the matrix.

BRIEF SUMMARY

The above-described needs associated with transparent composite articlesare specifically addressed and alleviated by the present disclosurewhich, in an embodiment, provides a composite article having an articlesurface and which includes a plurality of fibers at least partiallyembedded in a matrix. Each fiber may have at least one base surface anda pair of side surfaces oriented in non-perpendicular relation to thebase surface. The fibers may be positioned in side-by-side relation toone another.

Also disclosed is a method of manufacturing a composite articleincluding the steps of providing a plurality of fibers and forming thefibers with at least one base surface and a pair of side surfacesoriented in non-perpendicular relation to the base surface. The methodmay further include positioning the fibers such that the side surfacesoverlap one another when viewed along a direction normal to a plane ofthe layer.

In a further embodiment, disclosed is a fiber which may include at leastone base surface and a pair of side surfaces oriented innon-perpendicular relation to the base surface. The fiber may beembedded in a matrix.

The features, functions and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawingsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present disclosure will become moreapparent upon reference to the drawings wherein like numerals refer tolike parts throughout and wherein:

FIG. 1 is a perspective illustration of a composite article in anembodiment comprising a substantially optically transparent matrix and aplurality of substantially optically transparent fibers;

FIG. 2 is an exploded perspective illustration of the composite articleof FIG. 1 and illustrating a plurality of layers of the fibers;

FIG. 3 is an enlarged perspective illustration of a portion of thecomposite article of FIG. 1 and illustrating the arrangement of thelayers of fibers within the matrix and further illustrating sidesurfaces of each one of the fibers being oriented in non-perpendicularrelation to upper and lower surface of the fibers;

FIG. 4 is an enlarged sectional illustration of an embodiment of acomposite article and illustrating the fibers having side surfacesoriented in non-perpendicular relation to upper and lower surfaces andwherein the side surfaces of each layer are placed in close proximity tothe side surfaces of the immediately adjacent layers to minimize gapsbetween the side surfaces;

FIG. 5 is an enlarged partial sectional illustration taken along line 5of FIG. 4 and illustrating a plurality of light rays passing through acomposite article comprised of the matrix and fiber and illustratingminimal differences in the path lengths of the light passing through themain portion of the fibers relative to the light passing through theside surfaces of the fibers;

FIG. 6 is an enlarged illustration of a composite article having fiberswith side surfaces oriented perpendicularly relative to the articlesurface and having a relatively wide gap between the side surface andillustrating light rays having different optical path length due torefractive effects on the light rays that pass through the sidesurfaces;

FIG. 7 is an enlarged illustration of the composite article similar tothat which is illustrated in FIG. 6 and illustrating phase gratingeffects as a result of light rays passing between the fibers withoutgoing through the fibers resulting in phase differences with the lightthat passes through the fibers;

FIG. 8 is a sectional illustration of an embodiment of a compositearticle having layers arranged such that the gaps between the sidesurfaces of the fibers in one layer are offset from the gaps between theside surfaces of the fibers of adjacent layers;

FIG. 8A is a partial sectional illustration of a composite articlehaving fibers with non-planar side surfaces formed complementary to oneanother;

FIG. 9 is a sectional illustration of a further embodiment of acomposite article including fibers having a triangular cross section andarranged in alternating upright and inverted orientations and furtherillustrating the side surfaces of the adjacent fibers overlapping oneanother when viewed along a direction perpendicular to a plane of alayer;

FIG. 10A is a cross-sectional illustration of a fiber having aparallelogram cross-sectional shape;

FIG. 10B is a cross-sectional illustration of a fiber having atrapezoidal cross-sectional shape;

FIG. 10C is a cross-sectional illustration of a fiber having atriangular cross-sectional shape;

FIG. 10D is a cross-sectional illustration of the fiber having a diamondcross-sectional shape; and

FIG. 11 is an illustration of a flow chart including one or moreoperations that may be included in a methodology of manufacturing acomposite article.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating preferred and various embodiments of the disclosure, shownin FIGS. 1 and 2 is an embodiment of a composite article 10. Thecomposite article 10 may be fabricated as a fiber reinforced compositepanel 14 comprising a matrix 18 and a plurality of fibers 20 (FIG. 2)embedded within the matrix 18. The composite article 10 may befabricated as an optically transparent composite panel 14 such that thematrix 18 may comprise a substantially transparent polymeric matrix 18and the fibers 20 may comprise substantially transparent fibers 20.Although illustrated in FIG. 1 in a panel 14 configuration having planarpanel surfaces 16, the composite article 10 may be formed in any one ofa wide variety of sizes, shapes and configurations, without limitation,and may include planar surfaces and/or compound curvature surfaces.

Advantageously, the composite article 10 as disclosed herein includesfibers 20 having optimized shapes to improve the optical performance ofthe composite article 10. More specifically, the fibers 20 of thecomposite article 10 include side surfaces 28 (FIG. 3) that are orientedin non-perpendicular relation to one or more base surfaces 22 (FIG. 3)of a fiber 20. In the context of the present disclosure, a base surface22 of a fiber 20 comprises an upper and/or lower surface 24, 26 of thefiber 20. For example, referring briefly to FIGS. 10A-10B, the fiber 20is illustrated as having a parallelogram 42 cross section (FIG. 10A) ora trapezoidal 44 cross section (FIG. 10B) formed by two base surfaces 22and two side surfaces 28. The base surfaces 22 in FIG. 10A-10B comprisean upper surface 24 and a lower surface 26. FIG. 10C illustrates atriangular 46 cross section of the fiber 20 having a base surface 22 anda pair of side surfaces 28. FIG. 10D illustrates the fiber 20 in afurther embodiment comprising a diamond 48 cross-sectional shape havingonly side surfaces 28 and not having a base surface 22. It should benoted that although the fibers 20 shown in FIGS. 10A-10D are illustratedwith relative sharp corners, the present disclosure contemplates fibers20 of any configuration having corners that may be rounded, chamferedbeveled or otherwise provided as non-sharp corners.

Referring to FIG. 2, shown is an exploded illustration of the compositearticle 10 illustrating a plurality of fibers 20 formed as strips andarranged in layers 50 within the matrix 18. In an embodiment, the fibers20 may include one or more base surfaces 22 such as the upper and lowersurfaces 24, 26 of the fibers 20 illustrated in FIG. 4. As shown in FIG.2, the fibers 20 may be oriented within the matrix 18 such that the basesurfaces 22 (e.g., upper and lower surfaces 24, 26) are substantiallyparallel to an article surface 12 of the composite article 10 which mayimprove the optical performance of the composite article 10.

Although the composite article 10 is illustrated as having three layers50, any number may be provided. Furthermore, although FIG. 2 illustratesa cross-ply configuration 60 of the layers 50 wherein the fibers 20 ineach layer 50 as being oriented perpendicularly relative to the fibers20 of adjacent layers 50, the layers 50 may be arranged in aunidirectional configuration 58 as shown in FIG. 8 wherein the fibers 20of one layer 50 may be oriented parallel to the fibers 20 of adjacentlayers 50. Furthermore, the fibers 20 in a given layer 50 may beoriented at any angle (e.g., 15°, 22.5°, 45°, 60°, 75°, etc.) relativeto the fibers 20 of adjacent layers 50.

Referring to FIG. 3, shown is an enlarged perspective illustration of aportion of the composite article 10 illustrating the arrangement of thefibers 20 within the matrix 18. As can be seen in FIG. 3, each one ofthe fibers 20 includes upper and lower surfaces 24, 26 and opposing sidesurfaces 28 forming a parallelogram 42 (FIG. 10A) cross section.However, the fibers 20 may be formed in alternative shapes andconfigurations including a triangular 46 configuration illustrated inFIGS. 9 and 10C having a base surface 22 and a pair of side surfaces 28oriented in non-parallel relation to one another. In a furtherembodiment, the fiber 20 cross section may comprise a trapezoid 44 asillustrated in FIG. 10B, or a diamond 48 cross-sectional shape asillustrated in FIG. 10D and described in greater detail below. As may beappreciated, the fiber 20 may be provided in a wide variety ofcross-sectional shapes and is not limited to that which is illustratedin the Figures. Preferably, the fibers 20 have side surfaces 28 that areoriented non-perpendicularly relative to the base surfaces 22 and/ornon-perpendicularly to an article surface 12 of a composite article 10.

Referring to FIG. 4, shown is cross-sectional illustration of acomposite article 10 including fibers 20 each having side surfaces 28oriented in non-perpendicular relation to upper and lower surfaces 24,26 (i.e., base surfaces 22) of the fiber 20. As shown, the fibers 20 ofthe composite article 10 may be mounted in side-by-side arrangement andin relatively close proximity to one another to minimize the gap 36between the side surfaces 28 of adjacent fibers 20. By minimizing thegaps 36 between the side surfaces 28, distortion from phase differences86 (FIG. 7) in light passing through the fibers 20 relative to the lightpassing between the fibers 20 is minimized. By orienting the sidesurfaces 28 in non-perpendicular relation to the base surfaces 22 of thefibers 20 and by positioning adjacent fibers 20 in close proximity toone another, optical distortions due to diffractive and refractiveeffects and phase difference 86 (FIG. 7) are minimized. Advantageously,optical distortions are minimized even when the refractive index of thefiber 20 and matrix 18 varies over a given temperature range.Furthermore, as a result of the orientation of the side surfaces 28 andthe ability to position adjacent fibers 20 in close proximity to oneanother, the fiber 20 content of the composite article 10 may beincreased relative to the fiber 20 content of conventionalfiber-reinforced composites. The effect of the relatively closeside-by-side spacing of the fibers 20 may include an increase inmechanical performance of the composite article 10 without a significantreduction in optical performance.

As can be seen in FIG. 4, the fibers 20 with side surfaces 28 may beoriented in non-perpendicular relation to the upper and lower surfaces24, 26 of the fiber 20. The fibers 20 in each layer 50 are positioned inside-by-side arrangement to one another. In an embodiment, the fibers 20may be positioned such that the gap 36 between adjacent side surfaces 28is minimized. For example, the fibers 20 in a layer 50 may be positionedin side-by-side arrangement such that the side surfaces 28 overlap 38when viewed along a direction substantially normal to a plane of thelayer 52. In an embodiment, the adjacently disposed fibers 20 may bepositioned in sufficiently close proximity to one another such that thegap 36 between the side surfaces 28 is less than the fiber thickness 30.The close spacing of the fibers 20 minimizes the amount the incidentradiation 68 that may pass between the fibers 20 as described in greaterdetail below.

Referring again to FIG. 4, shown is the enlarged sectional illustrationof the composite article 10 illustrating three layers 50 of fibers 20wherein the fibers 20 of each layer 50 are positioned in side-by-siderelation to one another and in a manner such that the side surfaces 28of each fiber 20 are oriented substantially parallel to the sidesurfaces 28 of the immediately adjacent fibers 20. As indicated above,the fibers 20 are preferably positioned in side-by-side relationshipsuch that a relatively small gap 36 is formed between the side surfaces28 of adjacent fibers 20. The fibers 20 may be positioned such that theside surfaces 28 overlap 38 when viewed along a direction normal to aplane 52 defined by a layer 50 of the fibers 20.

The side surfaces 28 of each one of the fibers 20 may be orientedsubstantially parallel to one another to facilitate positioning ofadjacent fibers 20 in close proximity to one another althoughnon-parallel orientations of the side surfaces 28 are contemplated. Inan embodiment, the side surfaces 28 of the fibers 20 may be oriented atan angle θ (FIG. 10A) of between approximately 10° to 170° relative tothe upper and/or lower surfaces 24, 26 of the fibers 20. However, it iscontemplated that the side surfaces 28 may be oriented at angles θ ofless than 10° or greater than 170° relative to the upper and lowersurfaces 24, 26. In addition, the angle θ of the side surfaces 28 and/orthe angles θ of the side surfaces 28 of adjacently-disposed fibers 20may be varied among the fibers 20 within a layer 50 and/or among thefibers 20 in different layers 50 or in different portions of thecomposite article 10 as a means to minimize reduced optical performancethat may otherwise occur in conditions where light is oriented along adirection generally parallel to the angle θ of the side surfaces 28 andwhich may otherwise result in phase grating effects as described below.

The close proximity of the fibers 20 (FIG. 4) may minimize the amount ofradiation (e.g., light) passing through the gap 36 (FIG. 4) betweenadjacent fibers 20. In addition, differences in the optical path lengthsof light 72 (FIG. 5) passing through a given layer 50 (FIG. 4) can beminimized by minimizing the gap 36 between the fibers 20 of the layer50. By minimizing the gap 36 between adjacent fibers 20, the opticalpath length 72 of light passing through the main portion (i.e., betweenthe side surfaces 28) of each fiber 20 may be substantially similar tothe optical path length 72 of light passing through one or more of theside surfaces 28 of the fibers 20 in a layer 50 which results in minimaloptical distortion relative to fiber 20 arrangements of conventionalcomposites.

Referring still to FIG. 4, shown are three layers 50 of fibers 20wherein the uppermost layer 50 is comprised of fibers 20 formed in aparallelogram 42 cross section. Each one of the parallelogram 42 crosssection fibers 20 has upper and lower surfaces 24, 26 and opposing sidesurfaces 28 oriented substantially parallel to one another. FIG. 4 alsoillustrates a lowermost layer 50 comprised of fibers 20 having atrapezoidal 44 cross section. Each trapezoidal 44 cross section includesupper and lower surfaces 24, 26 and side surfaces 28 that are orientedin non-parallel relation to one another. The trapezoidal 44cross-sectional fibers 20 in the lowermost layer 50 of FIG. 4 may bearranged in alternating upright and inverted orientations such that theside surfaces 28 of adjacent fibers 20 are substantially parallel to oneanother.

Referring still to FIG. 4, the intermediate layer 50 between theuppermost layer 50 and lowermost layer 50 may be comprised of fibers 20having cross-sectional shapes similar to that of the fibers 20 in theuppermost or lowermost layers 50 although the fibers 20 in theintermediate layer 50 may have a different cross-sectional shape. Theintermediate layer 50 between the uppermost and lowermost layers 50 mayalso be oriented perpendicularly relative to the orientation of thefibers 20 in the uppermost layer 50 and lowermost layer 50 as shownwherein the fiber axis 34 extends along the plane 52 of the paper.

However, the intermediate layer 50 may be oriented perpendicularlyrelative to the orientation of the fibers 20 in the uppermost andlowermost layers 50. In addition, the fibers 20 in any of the layers 50may be oriented substantially parallel to the article surfaces 12 of thecomposite article 10. For example, the upper and lower surfaces 24, 26of the fibers 20 in FIG. 4 are illustrated as being orientedsubstantially parallel to the article surfaces 12. In addition, althoughthe base surfaces 22 (e.g., upper and lower surfaces 24, 26) of thefibers 20 are preferably substantially planar as illustrated in FIG. 4,the upper and/or lower surfaces 24, 26 of one or more of the fibers 20may be non-planar including slightly curved shapes of the upper and/orlower surfaces 24, 26. However, a substantially planar shape is believedto be preferable to minimize optical distortion.

Referring to FIG. 5, shown is an enlarged sectional illustration of thecomposite article 10 and a pair of fibers 20 located in relatively closeproximity to one another and further illustrating a plurality of lightrays 70 passing through the composite article 10. It can be seen thatthe path lengths 72 of the light rays 70 differ depending on whether thelight rays 70 pass through the main portion of the fiber 20 (i.e.,between the side surfaces 28) or whether the light rays 70 pass throughone or more of the side surfaces 28 of the fibers 20. For example, FIG.5 illustrates a first light ray 70A which passes from the matrix 18 intothe fiber 20 and then exits the fiber 20 and passes into the matrix 18resulting in a change in direction of the first light ray 70A due todifferences in refractive index of the matrix 18 relative to therefractive index of the fiber 20. Likewise, a fifth light ray 70E passesfrom the matrix 18 into the fiber 20 and then exits the fiber 20 suchthat the fifth path length 72E is substantially equivalent in length tothe first path length 72A of the first light ray 70A.

FIG. 5 also illustrates a third light ray 70C which passes through thematrix 18 into a side surface 28 of one of the fibers 20 and thencrosses the gap 36 and enters the side surface 28 of the adjacent fiber20 prior to exiting the fiber 20 and entering the matrix 18 along athird path length 72C. Advantageously, by minimizing the gap 36 betweenthe side surfaces 28, the difference in the third path length 72Crelative to the first and fifth path lengths 72A, 72E is relativelysmall. The second and fourth light rays 70B, 70D are incident upon oneof the side surfaces 28 of one of the fibers 20 resulting in longeroptical paths relative to the first, third and fifth path lengths 72A,72C, 72E. Although a difference in optical path length 72 generallyresults in optical distortion, in the arrangement of FIG. 5, the amountof light passing through the end portions may be kept relatively smallby minimizing the width of the gaps 36 and the total quantity of gaps 36in each layer 50 such that optical distortion is minimized.

Referring to FIG. 6, shown is an arrangement of a composite article 10′wherein the side surfaces 128 of a pair of fibers 120 are orientedgenerally perpendicularly relative to the upper and lower surfaces 124,126 of the fibers 120. The perpendicular orientation of the sidesurfaces 128 results in the side surfaces 128 of each one of the fibers120 acting as a prism when viewed off-angle or along a directionnon-parallel to the side surfaces 128. In this regard, FIG. 6illustrates a plurality of light rays 76 passing through the compositearticle 10′. It can be seen in FIG. 6 that the optical path lengths 78of the light rays 76 differ significantly depending on whether the lightrays 76 pass through the main portion of the fiber 120 (i.e., betweenthe side surfaces 128) or whether the light rays 76 pass through one ormore of the side surfaces 128 of the fibers 120. For example, FIG. 6illustrates a first and fourth light ray 76A, 76D passing from thematrix 118 into the fiber 120 at the upper surfaces 124 and then exitingthe fiber 120 and passing back into the matrix 118 at the lower surfaces126 resulting in a change in direction of the first and fourth light ray76A, 76D due to differences in refractive index of the matrix 18relative to the refractive index of the fiber 120.

FIG. 6 also illustrates a second light ray 76B entering one of thefibers 120 at a side surface 128 and then exiting the same fiber 120 atthe lower surface 126 of the fiber 120 resulting in relatively smallchange in direction and a correspondingly small difference in a secondpath length 78B relative to the first and fourth path lengths 78A, 78D.However, FIG. 6 illustrates a third light ray 76C entering the fiber 120at an upper surface 124 and then exiting the same fiber 120 at the sidesurface 128 resulting in a significant change in direction and asignificant difference in a third path length 78C of the third light ray76C relative to the first, second and fourth path lengths 78A, 78B, 78D.The net effect of the significantly large third path length 78C relativeto the first, second and fourth path lengths 78A, 78B, 78D in FIG. 6 isa significant reduction in optical performance due to refractive anddiffractive effects caused by the side surfaces 128 of the fibers 120.

Referring to FIG. 7, shown is the arrangement of the composite article10′ similar to that which is illustrated in FIG. 6 wherein the sidesurfaces 128 in FIG. 7 are oriented perpendicularly and are spaced apartfrom one another result in a relatively large spacing or gap 136 betweenthe side surfaces 128. The effect of the gap 136 between the sidesurfaces 128 is a reduction in optical performance due to phase gratingeffects. The phase grating effects reduce the optical performance of thecomposite article 10′ as a result of a portion of the light rays 80along direction 81 passing through the gap 136 and the remaining portionof the light rays 80 passing through both the matrix 118 and the fibers120, each of which may have different indices of refraction. In thisregard, the gap 136 allows the second light ray 80B to pass between theside surfaces 128 without passing through the fibers 120 which have adifferent index of refraction relative to the index of refraction of thematrix 118.

As known in the art, index of refraction or refractive index,represented by n(λ,T), is a function of the wavelength λ of radiationincident 68 on a material at temperature T. The refractive index of agiven material at a given temperature T may be defined as the ratio ofthe speed of light at a given wavelength λ in a vacuum to the speed oflight at the same wavelength λ in the given material at the temperatureT. Although the fibers 120 and matrix 118 may be selected of materialhaving the same refractive index at a given match point temperature fora given wavelength, the refractive indices of the respective materialsmay change or diverge from one another as the temperature changes (i.e.,increases or decreases) from the match point temperature.

As a result, in FIG. 7, the wavelength 82 of light passing through thefibers 120 will be different than the wavelength 84 of light passingthrough the matrix 118. As can be seen in FIG. 7, the phases of thefirst and third light rays 80A, 80C change as the first and third lightrays 80A, 80C pass from the matrix 118 into the fiber 120 and thenchange again as the first and third light rays 80A, 80C pass from thefiber 120 back into the matrix 118. However, the phase of the secondlight ray 80B passes between the fibers 120 and does not pass throughthe fibers 120 and therefore maintains the same phase. As a result, thephase of the second light ray 80B is different than the phase of thefirst and third light rays 80A, 80C which results in significant opticaldistortion in the composite article 10.

In contrast, FIG. 5 illustrates the advantageous embodiment of thefibers 20 as disclosed herein wherein the fibers 20 have angled sidesurfaces 28 that overlap 38 (FIG. 4) one another such that phasedifferences 86 (FIG. 7) in the light rays 70 passing through the fibers20 (i.e., phase grating effects) are minimized. Furthermore, thenon-perpendicular orientation of the side surfaces 28 coupled with theclose proximity of the side surfaces 28 results in minimal differencesin the distance that each first light ray 70A travels through the fiber20 material relative to the distance that each light ray 70 travelsthrough the matrix 18. The minimal differences in the optical pathlengths 72 of the light rays 70 in FIG. 5 result in minimal opticaldistortion from refractive or diffractive effects. Advantageously, theconfiguration of fibers 20 as disclosed herein also minimizes opticaldistortion despite differences in refractive index between the fibers 20and the matrix 18 wherein the magnitude of the differences in refractiveindex of the fibers 20 and the matrix 18 may increase with changes intemperature of the composite article 10.

In an embodiment, the composite article 10 as disclosed herein mayinclude fibers 20 having a refractive index that is substantiallyequivalent to the matrix 18 refractive index within a wavelength band ofinterest. More specifically, the matrix 18 and the fibers 20 preferablyhave complementary or substantially equivalent refractive indices withina broad temperature range for a wavelength band of interest. Thewavelength band of interest may include the visible spectrum and/oralternatively include the infrared spectrum or any other wavelengthband. In an embodiment, the refractive indices of the matrix 18 and thefibers 20 are preferably substantially equivalent or closely matchedwithin the wavelength band of interest for a given temperature range inorder to minimize or reduce bending of light at the interface of thematrix 18 and the fibers 20.

Referring still to FIG. 5, the matrix 18 and the fibers 20 may also beselected to have substantially equivalent temperature coefficients ofrefractive index dn(λ,T)/dT wherein dn(λ,T)/dT is the partial derivativeof index of refraction n(λ,T) with respect to temperature T. Thetemperature coefficient of refractive index dn(λ,T)/dT of a material maybe defined as the change in refractive index for the material for agiven wavelength with change in temperature of the material. In thepresent disclosure, the matrix 18 and fibers 20 preferably havesubstantially equivalent refractive indices within a broad temperaturerange for a wavelength band of interest such that the respectivetemperature coefficients of refractive index are also substantiallyequivalent. In an embodiment, the refractive indices and the temperaturecoefficients of refractive index of the matrix 18 and the fibers 20 arepreferably such that the refractive indices of the matrix 18 and thefibers 20 are equivalent at a given wavelength within the wavelengthband of interest for at least one temperature within a temperaturerange.

Referring now to FIG. 8, shown is a sectional illustration of acomposite article 10 including fibers 20 having a parallelogram 42 crosssection wherein the side surfaces 28 are substantially parallel to oneanother. The composite article 10 includes a pair of layers 50 includinga first layer 54 and a second layer 56 each having fibers 20 arranged inside-by-side relation to one another. As can be seen in FIG. 8, thefibers 20 are positioned such that the side surfaces 28 of each fiber 20are oriented substantially parallel to the side surfaces 28 of theimmediately adjacent fibers 20. The first layer 54 is positionedrelative to the second layer 56 such that the gaps 36 in the sidesurfaces 28 of the fibers 20 of the first layer 54 are offset 40 fromthe gaps 36 in the side surfaces 28 of the fibers 20 of the second layer56 when viewed along a direction substantially normal to the plane 52 ofat least one of the first and second layers 54, 56. By staggering oroffsetting 40 the gaps 36 of one layer 50 relative to other layers 50,optical distortion is spread throughout the composite article 10 therebyminimizing optical distortion at any single point within the compositearticle 10.

Referring to FIG. 8A, shown is a partial sectional illustration of apair of adjacently disposed fibers 20 having side surfaces 28 formed innon-planar configurations. In an embodiment, the side surfaces 28 may beformed as a pair of mating curved surfaces as illustrated in FIG. 8A. Asshown, the side surfaces 28 may be slightly curved and may be formedcomplementary to one another such as in a mating configuration 29. Inthe non-limiting example of FIG. 8A, the side surfaces 28 are formed ina mating configuration 29 wherein one of the side surfaces 28 has aconcave shape and the adjacent one of the side surfaces 28 has a convexshape that is sized and configured complementary to the concave shape.Although FIG. 8A illustrates fibers 20 having non-planar side surfaces28 being formed with a single curvature, the side surfaces 28 may beprovided in complex curvatures and are not limited to the matingconfiguration 29 shown. In an embodiment, fibers 20 with non-planar sidesurfaces 28 may be positioned in relatively close proximity to oneanother such that line of sight between the non-planar side surfaces 28is prevented. In this manner, phase grating effects as illustrated inFIG. 7 may be significantly reduced or eliminated for the fiber 20configuration illustrated in FIG. 8A due to light rays (not shown) thatmay enter between the gap 36 (FIG. 8) at the upper or lower surface 24,26 of the fibers 20 necessarily passing through at least a portion ofthe fiber 20 side surfaces 28 as opposed to the embodiment illustratedin FIG. 7 wherein light rays 80 (FIG. 7) may pass between the fibers 120(FIG. 7) without passing through the fibers 120 resulting in phasedifferences with the light that passes through the fibers 120 asdescribed above.

Referring to FIG. 9, shown is an embodiment of the composite article 10wherein the fibers 20 have a triangular 46 cross-sectional shape. Thetriangular 46 fibers 20 in a given layer 50 may be arranged inalternating upright and inverted orientations such that the sidesurfaces 28 of adjacent fibers 20 are substantially parallel to oneanother. Each one of the triangular 46 cross-sectional fibers 20 in FIG.9 has side surfaces 28 that are of equal length and which are orientedat equal angles relative to one forming an isosceles triangle. However,the triangular 46 cross-sectional fibers 20 illustrated in FIG. 9 may beprovided in a variety of different arrangements and are not limited tohaving substantially equivalent angles of the side surfaces 28.

As shown in FIG. 9, the fibers 20 are oriented such that gaps 36 betweenthe side surfaces 28 are minimized as a result of the overlap 38 of theside surfaces 28. FIG. 9 illustrates an arrangement of the layers 50where the first and second layers 54, 56 represent a cross-plyconfiguration 60 wherein the fibers 20 of one layer 50 are orientedperpendicularly to the fiber axis 34 or fibers 20 of the adjacent layer50. However, the layers 50 may be arranged in any orientation relativeto one another including a unidirectional configuration 58 wherein thefibers 20 of a given layer 50 are substantially parallel to the fibers20 of an adjacent layer 50.

Referring to FIGS. 10A-10D, shown are different cross-sectionalconfigurations of non-limiting embodiments of the fibers 20. FIG. 10Aillustrates the parallelogram 42 cross section of the fiber 20 havingupper and lower surfaces 24, 26 and substantially parallel side surfaces28. As can be seen in FIG. 10A, the fiber 20 has a generally elongatedcross-sectional shape which is preferably formed with a relatively highaspect ratio to minimize the quantity of gaps 36 (FIG. 4) in a layer 50(FIG. 4). The aspect ratio of a fiber 20 may be defined as the ratio offiber width 32 to fiber thickness 30. In an embodiment, the aspect ratiomay vary from approximately 3 to approximately 500 although the fiber 20cross section may have any aspect ratio of any value.

The fiber thickness 30 may be in the range of from approximately 5microns to approximately 5,000 microns (0.0002 to 0.20 inch). However,the fiber 20 may be provided in any fiber thickness 30, withoutlimitation. As shown in FIG. 10A, the side surfaces 28 are formed at anangle θ which may be in the range of from approximately 10° toapproximately 170° relative to the upper and/or lower surfaces 24, 26 ofthe fiber 20 although larger or smaller angles are contemplated.Although FIG. 10A illustrates the upper and lower surfaces 24, 26 asbeing substantially planar, the upper and lower surfaces 24, 26 may beslightly curved including slightly concave, slightly convex or crownedand are not limited to a strictly substantially planar or flat profile.

Referring to FIG. 10B, shown is a further embodiment of a fiber 20illustrated in the trapezoidal 44 cross section and having substantiallyplanar upper and lower surfaces 24, 26 being substantially parallel toone another. The side surfaces 28 are illustrated as being oriented innon-parallel relation to one another. The side surfaces 28 may beoriented at substantially equal angles relative to the upper and lowersurfaces 24, 26 but may extend in different directions. The trapezoidal44 cross section of the fiber 20 in FIG. 10B may be provided with arelatively high aspect ratio similar to that described above for theparallelogram 42 cross sectional fiber 20 of FIG. 10A and which mayresult in improved optical performance for the composite article 10.

Referring to FIG. 10C, shown is an embodiment of a fiber 20 in thetriangular 46 cross section having a base surface 22 and a pair of sidesurfaces 28 oriented in non-parallel relation to one another asdescribed above. A layer 50 of triangular 46 cross-sectional fibers 20may be arranged in side-by-side arrangement as shown in FIG. 9 in amanner to minimize the gap 36 between the side surfaces 28 of adjacentfibers 20. The aspect ratio of the triangular 46 cross-sectional fiber20 is preferably large to minimize distortion. Advantageously, thetriangular 46 cross section of the fiber 20 may facilitate registrationor alignment of the fibers 20 relative to one another when laying up thecomposite article 10. For example, a row of the triangular 46cross-sectional fibers 20 may be arranged in an upright orientation andin side-by-side arrangement to one another similar to that which isillustrated in FIG. 9. Following the laying up of the row of uprighttriangular 46 cross-sectional fibers 20, a row of inverted triangular 46cross-sectional fibers 20 may then be nested between the triangular 46cross-sectional fibers 20 to form a layer 50 of fibers 20 similar tothat illustrated in FIG. 9.

Referring to FIG. 10D, shown is a fiber 20 in a further embodimentcomprising a diamond 48 cross-sectional shape. As can be seen in FIG.10D, the diamond 48 cross-sectional shape fiber 20 may include two pairsof the side surfaces 28 in contrast to the single pair of side surfaces28 for the fibers 20 illustrated in FIGS. 10A-10C. The diamond 48cross-sectional shape fiber 20 illustrated in FIG. 10D may be arrangedin layers 50 (FIG. 9) by orienting each one of the fibers 20 such thatthe side surfaces 28 are oriented non-parallel to the article surface 12of the composite article 10.

Advantageously, in each one of the fiber 20 embodiments, thenon-perpendicular orientation of the side surfaces 28 relative to theupper and lower surfaces 24, 26 or base surfaces 22 facilitatesincreased fiber 20 volume in the composite article 10 relative to fiber20 volumes of fibers 20 having rounded side surfaces 28. In anembodiment, the composite article 10 may be configured such that thetotal volume of fibers 20 relative to the total volume of the compositearticle 10 may be in the range of from approximately 10% up toapproximately 90% or more. However, the volume of fibers 20 may compriseany portion of the total volume of the composite article 10. The desiredfiber 20 volume may be selected based up on a variety of parametersincluding, but not limited to, optical performance, strength, ballisticperformance, stiffness, weight and a variety of other factors.

The matrix 18 and the fibers 20 (FIGS. 1-5 and 8-9) may be formed of anysuitable material including, but not limited to, thermoplastics,thermosets, ceramics, and glass. Both the fibers 20 and the matrix 18are preferably formed of materials that are substantially opticallytransparent although the materials may comprise opaque materials. Inthis regard, the fibers 20 and the matrix 18 may be formed of materialhaving any level of transparency ranging from substantially transparentto substantially opaque. Thermoplastic materials from which the matrix18 and the fibers 20 may be formed may include at least one of thefollowing: acrylics, fluorocarbons, polyamides, polyethylenes,polyesters, polypropylenes, polycarbonates, polyurethanes,polyetheretherketone, polyetherketoneketone, and polyetherimides. Thematrix 18 and fibers 20 may also be formed of thermoset materials whichmay comprise at least one of the following: polyurethanes, phenolics,polyimides, bismaleimides, polyesters, epoxies, and silsesquioxanes. Inaddition, the matrix 18 and/or fibers 20 may be formed of inorganicmaterials including, but not limited to, carbons, silicon carbide andboron. The matrix 18 and the fiber fibers 20 may also be formed of glasscompositions which may include, without limitation, E-glass(alumino-borosilicate glass), S-glass (alumino silicate glass), puresilica, borosilicate glass, optical glass, ceramics, and glass-ceramicssuch as ROBAX™ glass-ceramic material.

The composite article 10 (FIGS. 1-5 and 8-9) may be configured in anyone of a variety of configurations including the panel 14 configurationillustrated in FIG. 1 or other configurations including, but not limitedto, a transparency for a vehicle such as a windshield, a canopy orwindow of an aircraft. In addition, the composite article 10 may beconfigured for use in alternative vehicular applications as well asnon-vehicular applications. For example, the composite article 10 may beconfigured as a structural panel or an architectural panel for abuilding. The composite article 10 may be configured for use instructural or non-structural applications. In this regard, the compositearticle 10 may be configured for use in any application, system,subsystem, structure, apparatus and/or device, without limitation.

Referring to FIG. 11, shown is a flow chart illustrating one or moreoperations that may be included in a methodology for manufacturing acomposite article 10 (FIGS. 1-5 and 8-9). Step 302 of the methodologymay include providing a plurality of fibers 20 (FIG. 2). As indicatedabove, the fibers 20 may be provided in any one of a variety ofsubstantially optically transparent materials. The fiber 20 material maybe selected to have a substantially equal temperature coefficient ofrefractive index as the matrix 18 (FIGS. 1-5 and 8-9) in order tominimize optical distortion as the temperature of the composite article10 changes.

Step 304 of the methodology of FIG. 11 may include forming the fibers 20with at least one base surface 22 (FIG. 4) and a pair of side surfaces28 (FIG. 4) oriented non-perpendicularly relative to the base surface22. The fibers 20 may be oriented in any one of a variety of alternativecross-sectional shapes including, but not limited to, those which areillustrated in FIGS. 10A-10D. The cross-sectional shapes may include thebase surface 22 such as the upper and lower surfaces 24, 26. Each one ofthe fiber 20 configurations also includes at least one pair of the sidesurfaces 28 which are oriented in non-perpendicular relation to the basesurface 22 as illustrated in FIGS. 10A-10C. The side surfaces 28 may beoriented at an angle θ (FIG. 10A) of between approximately 10° and 170°relative to the base surface 22 and/or relative to the upper and lowersurfaces 24, 26 although larger or smaller angles are contemplated.

Step 306 of the methodology of FIG. 11 may include embedding the fibers20 in a matrix 18. The matrix 18 may preferably comprise a substantiallyoptically transparent material similar to that which was describedabove. Furthermore, the matrix 18 material is preferably of asubstantially equivalent temperature coefficient of refractive index tothat of the fibers 20 as indicated above.

Step 308 of FIG. 11 may include orienting the fibers 20 such that thebase surface 22 and/or the upper and lower surfaces 24, 26 aresubstantially parallel to the article surface 12 of the compositearticle 10. For example, FIG. 4 illustrates the arrangement of thefibers 20 in substantially parallel orientation to the article surface12. Likewise, FIG. 9 illustrates a plurality of triangular 46cross-sectional shaped fibers 20 having base surfaces 22 which may eachbe oriented substantially parallel to a substantially planar articlesurface 12.

Step 310 of the methodology of FIG. 11 may include arranging the fibers20 such that the side surfaces 28 are oriented non-perpendicularlyrelative to the article surface 12. For example, FIGS. 4, 8 and 9illustrate the fibers 20 arranged in side-by-side relation to oneanother such that the gap 36 between the side surfaces 28 is oriented innon-perpendicular relation to the article surface 12. By orienting theside surfaces 28 at an angle (i.e., non-perpendicularly) relative to thearticle surface 12, the amount of light passing between the sidesurfaces 28 is minimized.

Step 312 of the methodology of FIG. 11 may comprise positioning thefibers 20 in side-by-side relation to one another to form a layer 50 ofthe fibers 20. The fibers 20 are preferably positioned such that theside surfaces 28 of each fiber 20 are substantially parallel to the sidesurfaces 28 of the immediately adjacent fibers 20 as illustrated inFIGS. 4, 8 and 9. Such an arrangement will reduce optical distortion andthereby improve the optical performance of the composite article 10.

Step 314 of FIG. 11 may include positioning the fibers 20 in closeproximity to one another to minimize the gap 36 between the sidesurfaces 28. The side surfaces 28 preferably overlap 38 (FIG. 4) oneanother when viewed along a direction substantially normal to a plane ofthe layers 52 (FIG. 4). As shown in FIG. 5, the fibers 20 are positionedin close proximity to one another to minimize the width of the gap 36between the side surfaces 28 and provide an arrangement where the lengthof the optical paths of light passing through the main portion of thefibers 20 is substantially equivalent to the length of the optical pathspassing through one or more of the side surfaces 28 of the fibers 20. Inthis manner, phase differences 86 (FIG. 7) are minimized and such thatoptical distortion is minimized.

Step 316 of the methodology of FIG. 11 may comprise curing orconsolidating the matrix 18 material and/or the fibers 20 material inorder to reduce the composite article 10 (FIGS. 1-5 and 8-9). Heatand/or pressure may be applied to the composite article 10 for curingthe matrix 18 and/or the fibers 20. In addition, any one of a variety ofintermediate steps including debulking and degassing may be performedprior to curing or consolidating the matrix 18 and/or fiber 20 material.

Additional modifications and improvements of the present disclosure maybe apparent to those of ordinary skill in the art. Thus, the particularcombination of parts described and illustrated herein is intended torepresent only certain embodiments of the present disclosure and is notintended to serve as limitations of alternative embodiments or deviceswithin the spirit and scope of the disclosure.

What is claimed is:
 1. A method of manufacturing a composite article,comprising the steps of: providing a plurality of fibers, at least aportion of the plurality of fibers being optically transparent; formingthe fibers with at least one base surface and a pair of side surfacesoriented in non-perpendicular relation to the base surface; positioningthe fibers in a layer in side-by-side relation to one another such thatthe side surfaces overlap one another when viewed along a directionnormal to a plane of the layer; and embedding the fibers at leastpartially in an optically transparent polymeric matrix.
 2. The method ofclaim 1 further comprising the step of: orienting the fibers such thatthe base surface is substantially parallel to an article surface of thecomposite article.
 3. The method of claim 1 further comprising the stepof: positioning the fibers in the layer such that the side surfaces ofthe fibers are substantially parallel to side surfaces of immediatelyadjacent fibers.
 4. The method of claim 1 wherein: the side surfaces ofan adjacent pair of fibers are non-planar; and the fibers beingpositioned such that line of sight through a gap between the sidesurfaces is prevented.
 5. The method of claim 1 wherein: the sidesurfaces of an adjacent pair of fibers have mating curved surfaces. 6.The method of claim 1 wherein: the plurality of fibers are arranged in afirst layer and a second layer; and the first layer being positionedrelative to the second layer such that gaps between the side surfaces ofthe fibers of the first layer are offset from the gaps between the sidesurfaces of the fibers of the second layer.
 7. The method of claim 1wherein: the fibers have a triangular cross sectional shape.
 8. Themethod of claim 1 wherein: the base surface comprises an opposing pairof upper and lower surfaces; and the side surfaces of at least a portionof the fibers are substantially parallel to one another.
 9. The methodof claim 1 wherein: the base surface comprises an opposing pair of upperand lower surfaces; and the side surfaces of at least a portion of thefibers are oriented in non-parallel relation to one another.
 10. Themethod of claim 1 wherein: the fibers have an elongated cross sectionwith an aspect ratio of fiber width to fiber thickness; and the aspectratio being in a range of from approximately 3 to approximately
 500. 11.The method of claim 10 wherein: the fiber thickness is in a range offrom approximately 5 microns to approximately 5000 microns.
 12. Themethod of claim 1 wherein: the fiber having a refractive index that issubstantially equivalent to a matrix refractive index within awavelength band of interest.
 13. The method of claim 12 wherein: thematrix and the fiber have substantially equivalent temperaturecoefficients of refractive index.
 14. The method of claim 1 wherein atleast one of the matrix and the fiber is formed from at least one of thefollowing materials: a thermoplastic material comprising at least one ofthe following: acrylics, fluorocarbons, polyamides, polyethylenes,polyesters, polypropylenes, polycarbonates, polyurethanes,polyetheretherketone, polyetherketoneketone, polyetherimides; athermoset comprising at least one of the following: polyurethanes,phenolics, polyimides, bismaleimides, polyesters, epoxies,silsesquioxanes; inorganic material comprising at least one of thefollowing: carbons, silicon carbide, boron; and glass comprising E-glass(alumino-borosilicate glass), S-glass (alumino silicate glass), puresilica, borosilicate glass, optical glass, ceramics, glass ceramics. 15.A method of manufacturing a composite article, comprising the steps of:providing a plurality of fibers, at least a portion of the plurality offibers being optically transparent; forming at least a portion of thefibers with an opposing pair of substantially parallel upper and lowersurfaces and a pair of side surfaces oriented in non-perpendicularrelation to at least one of the upper and lower surfaces; positioningthe fibers in a layer in side-by-side relation to one another such thatthe side surfaces overlap one another when viewed along a directionnormal to a plane of the layer and such that a gap between the sidesurfaces is less than a fiber thickness; and embedding the fibers atleast partially in an optically transparent polymeric matrix.